In recent years, imaging devices capable of capturing images in various directions such as a celestial sphere image, an omnidirectional image, or a panorama image have been developed, and systems in which the image captured using such an imaging device is displayed on a display unit of a PC, a tablet terminal, a mobile terminal, a head mount display (HMD), or the like, and an image selected by the user or an image automatically selected in accordance with a direction of the user can be observed are widely used.
For example, in the PC or the like, it is possible to acquire video (moving image) data of an omnidirectional image of a 360° range from an external server or read it from a recording medium and cause it to be displayed on the display device. The user is able to select an image in an arbitrary direction, cause the selected image to be displayed on the display device, and observe an image such as a moving image or a still image while changing a viewpoint freely.
The image displayed on the display unit of the PC, the tablet terminal, or the mobile terminal can be displayed in an observation direction moved by a mouse operation of the user or a slide process, a flick process, or the like performed on a touch panel, and the user is able to easily enjoy the image in various directions.
In a case where an image is displayed on the head mount display (HMD), it is possible to display an image according to a direction of the head of the user in accordance with sensor information obtained by detecting a motion or a direction of the head mounted on the HMD, and the user is able to feel as if the user were in the image displayed on the display unit of the HMD.
Such image display devices mostly have a function of outputting an audio together with an image.
In most of devices of a related art which output an image and an audio, a scheme of any one of the following types (a) and (b) is employed as an audio output control scheme:
(a) An image following type audio control scheme in which control is performed such that an audio listening direction is moved in accordance with movement of the observation image to follow an observation image.
(b) An image non-following type audio control scheme in which control is performed such that an audio listening direction is fixed regardless of movement of an observation image.
As described above, as the audio control scheme in the device of the related art, either (a) the image following type audio control scheme or (b) the image non-following type audio control scheme is often employed.
Further, (a) the image following type audio control scheme is disclosed, for example, in Patent Document 1 (Japanese Patent Application Laid-Open No. 2002-345097).
As an audio output together with an image, for example, in addition to an audio generated from a subject (object) included in the image, audios which are not generated by the subject in the image such as narration such as explanation of an image, comments, BGM and the like are included.
In the case of the audio generated from the subject in the image, a realistic feeling increases when the audio listening direction is moved with the movement of the image.
On the other hand, in the case of the audios which are not generated by the subject in the image such as narration such as explanation of an image, comments, and BGM, it is comfortable to hear if they are heard consistently in a fixed direction.
However, if control is performed such that an audio to follow an image is distinguished from an audio not to follow an image, a process is complicated, and it is difficult to implement control.